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1
In a large skillet, heat the olive oil until shimmering.
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2
Add the onions, rosemary and a generous pinch of salt and cook over moderate heat, stirring occasionally, until soft and caramelized, 40 to 45 minutes.
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3
Stir in the vinegar and garlic and cook until the mixture is fragrant and the vinegar evaporates, about 2 minutes.
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4
Stir in the parsley and season with salt.
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5
Let cool completely.
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6
Discard the rosemary sprig.
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7
Meanwhile, roast the red pepper directly over a gas flame or under the broiler, turning, until charred all over.
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8
Transfer the pepper to a bowl, cover tightly with plastic wrap and let cool, about 15 minutes.
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9
Peel, stem and seed the pepper, then cut into thin strips.
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10
Preheat the oven to 375.
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11
Line a large rimmed baking sheet with parchment paper.
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12
On a lightly floured work surface, roll out the puff pastry to a 12-by-14-inch rectangle.
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13
Slide the pastry onto the parchmentlined baking sheet and poke it all over with a fork.
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14
Top with another sheet of parchment and a baking sheet and bake for 20 to 25 minutes, until the pastry is lightly browned.
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15
Remove the top baking sheet and parchment paper and bake the pastry for 15 minutes longer, until slightly puffed and browned.
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16
Let cool for 5 minutes.
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17
Spread the cooled onions evenly over the pastry, then top with the roasted pepper strips, anchovies and olives.
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18
Cut into squares and serve.
